1. Field of the Invention
The present invention relates to a light amount adjusting device for adjusting brightness and contrast of an image when a light source irradiates an image formed by an image forming device such as a Braun tube or a liquid crystal panel so that the image is projected on a screen through a projecting lens. The present invention also relates to a projector using the light amount adjusting device.
2. Description of the Prior Art
In a projector, an image such as a symbol and a picture is formed on an image forming device such as a Braun tube (i.e., CRT) or a liquid crystal panel, and a light source such as a halogen lamp irradiates the image, so that a projecting lens projects the image on a screen. The projector projects a still image such as a symbol image on a screen for a presentation, or a motion picture on a screen of a home theater system.
When such a projector is used in a rear projection television or a home theater system to project a movie requiring for a change of brightness in a wide range, it is possible to properly adjust brightness of an image of the movie. For example, the brightness may be reduced for a dark image and increased for a bright image to increase contrast, thereby obtaining a profound image.
When an image becomes bright and dark repeatedly, that is, brightness changes for every one several tenth seconds, a viewer may suffer eye fatigue and receive an optical stimulus, thereby causing a physical problem. Accordingly, it is necessary to adjust quantity of light for every frame of continuous images for reducing the stimuli on the eyes.
Patent Reference 1 (Japanese Patent Publication (Kokai) No. 2003-241311) has disclosed a conventional device for adjusting light quantity. In the reference, light from a light source is divided into three primary colors R, G and B through a dichroic mirror. When light is irradiated on an image forming panel such as a liquid crystal panel, a light quantity reducing device is arranged between the light source and the dichroic mirror. In the projector disclosed in the reference, light from the light source is divided into the three primary colors R, G and B, and the primary colors are irradiated on the image forming panels each formed of the liquid crystal panel. A projecting lens focuses light passing through the panels and projects an image on an outside screen.
As a method of forming an image, other than the liquid crystal panel, there is known a method (a CRT projector) in which a Braun tube emits scanning lines, or a digital imaging method (a digital light processing projector) in which a fine mirror transforms beams of the three primary colors R, G and B into scanning lines. In the light quantity reducing device, a substrate having an optical path opening aligned with a center of an optical axis is arranged in an optical path from the light source to the mirror. A plurality of blades is sequentially overlapped at a circumferential edge of the optical path opening of the substrate, and is arranged to be rotatable.
The blades are attached to the circumferential edge of the optical path opening with a predetermined spacing, and contour edge portions thereof are overlapped in a scale shape. Further, the blades are arranged such that leading end portions thereof face the optical path opening. When the blades rotate around end portions thereof, the leading end portions cover the optical path opening from a large aperture to a small aperture. Such a structure is widely known as a light amount adjusting device for a camera.
When such a structure widely known in a camera device, in which the plural blades are arranged around the optical path opening and rotate to adjust an aperture of the optical path opening, is adopted in a projector such as a projector, the following problems may occur.
In a typical projector, a light source irradiates light on an image forming device, and an image formed on the image forming device is projected on a screen. Accordingly, heat of the light source affects a blade member arranged between the light source and the screen. Especially, a recent projector needs to be small and have high brightness. Accordingly, a metal halide lamp or a high pressure mercury lamp having high brightness is used as the light source, so that a temperature around the lamp may reach 200 degrees. In such a case, the blade member may be formed of a thin metal plate made of SUS. As a result, it is necessary to drive the blame member with large load, thereby making it difficult to operate the blame member uniformly and reduce an operation noise.
When a metal rolled plate made of SUS is punched out to form the blade member and the blade member is assembled in the projector, a tip portion of the blade member may be curved as shown in FIG. 10, thereby making it difficult to operate the blame member uniformly. In an extreme case, the blade members may bit each other, thereby making it difficult to adjust quantity of light.
In the field of camera devices, for example, as disclosed in Patent Reference 2 (Japanese Utility Model (Kokai) No. 58-168715), there is known a shutter blade of a camera in which titanium, a titanium alloy, aluminum, or an aluminum alloy is deposited on a translucent film such as a polyimide film and a polyester film. However, there is no disclosure regarding that such a blade may be used as a heat resistant blade relative to heat of a light source of a projector in place of the metal sheet blade in the conventional projector. When such a material is used for a blade member of a projector device, the material needs to withstand heat of a light source of the projector. However, there is no disclosure regarding heat resistance of the material. Further, there is no disclosure regarding a configuration of a light amount adjusting device of the projector.